The present invention relates to boron nitride sealing members which are particularly suitable for sealing off an oxygen reference chamber with respect to a lambda-probe space containing exhaust gas, as well as a method for its manufacture.
Boron nitride (BN) gaskets, formed by machining from hot-pressed BN blocks made of hexagonal boron nitride material, fulfill the necessary resistance to gasoline, but are too expensive as a mass production product because of the costly manufacture.
The attached FIG. 1 shows schematically a lambda probe, known illustratively from the U.S. Pat. No. 5,571,379, which is situated in an exhaust-gas path of an internal combustion engine. The probe, designated generally by 10, is located within a housing 12 that is screwed into a flange 14 of an exhaust pipe 11 leading from the engine 13. Situated within a cylindrical zirconium-dioxide probe substrate 5 is an oxygen (O.sub.2) reference chamber 3 which projects into a porous part of housing 12 seated in exhaust pipe 11. So that the measuring results are not invalidated, a peripheral flange 4 of substrate 5 is sealed off with respect to housing 12 by gaskets 1,2 made of boron nitride, so that no exhaust gas 15 can reach oxygen reference chamber 3. As already mentioned, in the U.S. Patent indicated above, the BN gaskets are machined from hot-pressed boron nitride blocks, and thus have the disadvantage of the high production costs already described. It should be mentioned that the design of the oxygen sensor or of lambda probe 10, selected in FIG. 1 for the related art, can be implemented just the same with boron-nitride sealing members formed according to the invention, i.e., that the construction shown in FIG. 1 can also be used in conjunction with the invention.